1. Field of the Invention
The present invention relates to a method for molding a solid article containing one or more vulnerable inserts, and more particularly to a centrifugal casting method utilizing curable fluid material. The insert, which may be dimensionally unstable or otherwise easily damaged by heat, pressure or solvents, is incorporated according to the present invention as an integral part of the finished article, firmly adhering to the cured fluid material molded around it without distortion or damage to the insert.
2. Description of the Related Art
A rapidly expanding class of manufactured items includes articles molded to incorporate inserts which are significantly more susceptible to damage by heat, pressure, velocity or solvents than are the host articles themselves. One representative group of such inserts would be those that are dimensionally unstable, including, for example, flexible sheet inserts such as pressure bladders, and brittle objects such as glass or plastics. Another group of vulnerable inserts would include those whose dimensions may be stable, but whose functions would be impaired by the environmental excesses of the molding process. This group might include delicate electronic components, pharmaceuticals, heat-degradable organic materials and shock-sensitive explosives. A third group could be made up of inserts including those from groups one and two which may be sensitive to solvents and adhesives commonly used to adhere the matrix material to the insert in the assembly process after the components have been made separately. Additionally, many of these adhesives and solvents have been shown to be harmful to the external natural environment, and many countries have banned articles prepared using them. Fabricating articles without damaging or distorting such inserts has traditionally presented a formidable challenge.
Molding processes involving the flow of liquid material commonly employ high heat and pressure to effect the curing of the liquid. These processes may be entirely satisfactory for molding physically rugged or temperature-insensitive articles. However, elevated heat and pressure methods are unsuitable for articles incorporating inserts that are highly susceptible to damage or distortion during the molding process. Alternate molding methods such as reaction injection molding may avoid extremes of heat and pressure, but depend upon the addition of reactants at high velocity to insure uniform dispersion and more even catalysis. Here again, such velocity could distort the shape or endanger the functionality of a vulnerable insert.
Still another method, low pressure casting by gravity introduction of the curing liquid into the mold, may decrease the detrimental effect of the foregoing environmental extremes, but tends to trap bubbles within the finished article. Such random cavities are detrimental to the structural integrity of the article, and slowing the reaction process enough to preclude the formation of these cavities would render the process economically infeasible.
While the trapping of bubbles can be minimized by introducing the curing liquid centrifugally into the mold, the potential for damage to the inserts remains significant. For example, heat and pressure are of concern in traditional centrifugal methods just as in the other molding methods discussed, and equipment structures in all methods are typically bulky or heavy in order to be strong enough to withstand the high heats and pressures required.
Accordingly, it is an object of this invention to rapidly produce molded articles containing one or more dimensionally unstable or easily damaged inserts without damaging or distorting those inserts.
It is another object of this invention to provide solvent-free production embedding of vulnerable inserts into solid, foam or combination solid and foam articles of various configurations.